1. Field of the Invention
The present invention relates to a metal golf club head, more particularly, to a metal golf club head which ensures softness when hitting a ball and good control thereof, and has improved characteristics for accumulating impact resilient energy.
2. Description of the Prior Art
Generally, a metal golf club head is integrally formed from a metal such as a brass, stainless steel or the like. The club head of this type is designed to have a shape and a weight corresponding to the number given to the club. Such a club head is, however, a mass of metal and therefore tends to lack elasticity. In particular, the ball hitting surface of the iron head, which is the part most essential for hitting a ball, has a low elasticity which means there is a small coefficient of restitution of the surface, and this prevents the metal club head from exhibiting the softness on hitting a ball which is available with wood clubs as well as a long ball-hitting distance.
To obviate this problem, a metal golf club head has heretofore been known in which a synthetic resin layer reinforced by the incorporation of a carbon fiber or a glass fiber is formed on the surface of a head body, including the ball hitting surface, so as to increase the impact resilient force of the ball hitting surface. Such a metal golf club was disclosed in, for example, the specification of Japanese Utility Model Laid-Open No. 16670/1984.
According to this known golf club head, in order to attach and retain on the head body the reinforced synthetic resin layer formed on the head, the head is provided with a multiplicity of bores penetrating its metallic core material from the face side to the back side, and the reinforced synthetic resin layers formed on the face side and back side of the metallic core material are coupled together by means of the same synthetic resin material as is used on the face and back sides being charged into the above described bores.
Thus, due to the multiplicity of through bores formed in the metallic core material, the metal golf club head of this type suffers a problem in that the impact stress occurrring in the reinforced synthetic resin layer as a result of the impact when the ball is hit by the ball hitting surface of the head body is propagated through the coupling synthetic resin material in the through bores and absorbed by the reinforced synthetic resin layer on the back side. In other words, the impact resilient energy caused by the impact is attenuated, leaving no impact resilient energy stored in the face surface, which results in a decrease in the resilient force applied to a ball and, therefore, in the incapability of extending the distance over which a ball can be hit.
In the metal golf club head of the type disclosed in the specification of the above described Japanese Utility Model Laid-Open No. 16670/1984, an attempt has also been made to increase the ball hitting distance at the same time as exhibiting softness at the time of hitting a ball by employing a lighter club head in which the thickness of each part of the metallic head, including its face portion, is made thinner, and, in accordance with this improvement, by providing the head body with a synthetic resin layer which includes a reinforcing fiber.
As a result, as the portion of the head body which is made of metal becomes thinner and lighter in weight, this type of iron head involves another disadvantage in that the mechanical strength at the portion which joins the face portion and the hosel portion of the head body decreases, causing the jointing portion to become deformed, cracked or broken by the impact which occurs when the ball is hit.